fix removing cube data from cubeviz

[kecnry]

Description

This pull request fixes the case where removing data from a cube viewer in cubeviz would raise a traceback from the plugins through the spectral viewer. To reproduce: load cubeviz, open moment maps, calculate moment map (adding to viewer or not, does not matter), use the data-menu in the uncertainty viewer to remove the moment map. Previously this resulted in a callback from either line lists or line analysis.

Change log entry

• Is a change log needed? If yes, is it added to CHANGES.rst? If you want to avoid merge conflicts,
  list the proposed change log here for review and add to CHANGES.rst before merge. If no, maintainer
  should add a no-changelog-entry-needed label.

Checklist for package maintainer(s)

This checklist is meant to remind the package maintainer(s) who will review this pull request of some common things to look for. This list is not exhaustive.

• Are two approvals required? Branch protection rule does not check for the second approval. If a second approval is not necessary, please apply the trivial label.
• Do the proposed changes actually accomplish desired goals? Also manually run the affected example notebooks, if necessary.
• Do the proposed changes follow the STScI Style Guides?
• Are tests added/updated as required? If so, do they follow the STScI Style Guides?
• Are docs added/updated as required? If so, do they follow the STScI Style Guides?
• Did the CI pass? If not, are the failures related?
• Is a milestone set? Set this to bugfix milestone if this is a bug fix and needs to be released ASAP; otherwise, set this to the next major release milestone.
• After merge, any internal documentations need updating (e.g., JIRA, Innerspace)?

[codecov]

Codecov Report

Attention: 10 lines in your changes are missing coverage. Please review.

Comparison is base (0673de8) 91.54% compared to head (5ec8038) 91.55%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
jdaviz/core/template_mixin.py	93.27%	8 Missing ⚠️
...configs/cubeviz/plugins/moment_maps/moment_maps.py	90.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2608      +/-   ##
==========================================
+ Coverage   91.54%   91.55%   +0.01%     
==========================================
  Files         161      161              
  Lines       19757    19842      +85     
==========================================
+ Hits        18086    18166      +80     
- Misses       1671     1676       +5     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[rosteen]

Simple enough, I confirmed that the fix works. Thanks!

[pllim]

Tried with Gaussian Smooth and Moment Map. Didn't crash. Code looks like code.

Thanks!